Parylene is a generic name for members of a series of poly(p-xylylene) polymers. Parylene polymer is known to excel as a dielectric and as a water vapor barrier without being toxic. Having been commercialized in the 1960s, parylene has found widespread use in the electronics, automotive, aerospace, medical, and other industries. It generally has preferable chemical vapor depositing attributes compared to other conformal coating materials such as acrylics, epoxies, polyurethanes, and silicons. For example, some parylenes can be deposited in extremely thin layers that are relatively strong and essentially pinhole-free. It is precisely these depositing characteristics that make parylene useful in micro/nanofabrication.
FIGS. 1-4 are molecular structure diagrams of four types of parylene of the prior art.
FIG. 1 shows parylene N, the basic member of the series. It is commonly derived from [2.2]paracyclophane, which can be synthesized from p-xylene. Parylene N is typically a completely linear, highly crystalline material.
FIG. 2 shows parylene C, which has one chlorine group per repeat unit. It is typically produced from the same dimer as parylene N but having a chlorine atom substituted for one of the aromatic hydrogen atoms.
FIG. 3 shows parylene D, which has two chlorine groups per repeat unit. Although it has better diffusion characteristics than parylene C, parylene D generally deposits less uniformly than parylene C.
FIG. 4 shows parylene AF-4, with the alpha hydrogen atoms of the N dimer replaced with fluorine. Parylene AF-4 is also known as Parylene SF as manufactured by Kisco Conformal Coating, LLC of California (a subsidiary of Kisco Ltd. of Japan), and PARYLENE HT® as manufactured by Specialty Coating Systems, Inc. of Indianapolis, Ind.
Other parylenes, such as parylene VT-4, parylene A, parylene AM, and parylene X, are known in the art and are used for specialized products in industry.
Fundamental aspects of parylene N and parylene C are detailed in P. Kramer et al., “Polymerization of Para-Xylylene Derivatives (Parylene Polymerization). I. Deposition Kinetics for Parylene N and Parylene C,” Journal of Polymer Science: Polymer Chemistry Edition, Vol. 22 (1984), pp. 475-491. This journal article is hereby incorporated by reference in its entirety for all purposes.
Fundamental aspects of parylene X are detailed in J. Senkevich et al., “Thermomechanical Properties of Parylene X, A Room-Temperature Chemical Vapor Depositable Crosslinkable Polymer,” Chem. Vap. Deposition, 2007, 13, pp. 55-59. This journal article is hereby incorporated by reference in its entirety for all purposes.
Parylene C
Of the common types of parylene, parylene C is perhaps the most widely used in industry. Its ease of use and especially well-mannered chemical vapor deposition characteristics make it ideal for use as a conformal coating on printed circuit boards and as a structure or sacrificial intermediate in nanofabricated devices. Its demonstrated bio-compatibility as a United States Pharmacopeial Convention (USP) Class VI biocompatible polymer makes it suitable for medical devices.
Parylene C is sometimes referred to with a dash, i.e., “parylene-C,” and sometimes is abbreviated as “PA-C.”
Parylene C membrane substrates generally have strength and flexibility (e.g., Young's modulus≈4 GPa), conformal pinhole-free room-temperature deposition, a low dielectric constant (≈3), high volume resistivity (>1016 Ω-cm), transparency, and ease of manipulation using standard microfabrication techniques such as reactive ion etching (RIE).
A need exists in the art for better materials or more uses for old materials.